Math Problem Statement

What is the uncertainty of the area given the diameter

Solution

The uncertainty of the area of a circle, given its diameter, depends on both the uncertainty of the diameter measurement and how the uncertainty propagates through the formula for the area of a circle.

The area AA of a circle is related to the diameter DD by the formula: A=πD24A = \frac{\pi D^2}{4}

If the diameter DD has an uncertainty ΔD\Delta D, then the uncertainty in the area ΔA\Delta A can be estimated using error propagation. For functions like this, the relative uncertainty in the area is proportional to the relative uncertainty in the diameter.

To compute the uncertainty ΔA\Delta A, you use the following formula: ΔAA=2×ΔDD\frac{\Delta A}{A} = 2 \times \frac{\Delta D}{D} or equivalently, ΔA=A×2×ΔDD\Delta A = A \times 2 \times \frac{\Delta D}{D}

Steps:

  1. Calculate the area A=πD24A = \frac{\pi D^2}{4}.
  2. Calculate the relative uncertainty in the diameter ΔDD\frac{\Delta D}{D}.
  3. Multiply the relative uncertainty by 2.
  4. Finally, multiply by the area to find the uncertainty in the area ΔA\Delta A.

Example:

If the diameter of a circle is D=10cmD = 10 \, \text{cm} with an uncertainty ΔD=0.2cm\Delta D = 0.2 \, \text{cm}, the area and its uncertainty would be:

  1. A=π(10)24=78.54cm2A = \frac{\pi (10)^2}{4} = 78.54 \, \text{cm}^2
  2. Relative uncertainty in the diameter = 0.210=0.02\frac{0.2}{10} = 0.02
  3. Multiply by 2: 2×0.02=0.042 \times 0.02 = 0.04
  4. Uncertainty in area = 78.54×0.04=3.14cm278.54 \times 0.04 = 3.14 \, \text{cm}^2

Thus, the area is 78.54cm2±3.14cm278.54 \, \text{cm}^2 \pm 3.14 \, \text{cm}^2.

Would you like more details or have any questions?

Here are 5 related questions:

  1. How does uncertainty propagation work for other shapes?
  2. What is the uncertainty in the radius if only the diameter uncertainty is given?
  3. Can the uncertainty be reduced by improving the measurement of the diameter?
  4. How does uncertainty affect the volume of a sphere given its diameter?
  5. What are common methods to measure uncertainties in physical quantities?

Tip: When dealing with uncertainties, always try to express them in terms of relative percentages for easier comparison across different quantities.

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Math Problem Analysis

Mathematical Concepts

Error Propagation
Geometry
Uncertainty Measurement

Formulas

Area of a circle: A = (πD^2)/4
Uncertainty in area: ΔA = A * 2 * (ΔD / D)
Relative uncertainty: ΔA / A = 2 * (ΔD / D)

Theorems

Error Propagation Theorem

Suitable Grade Level

Grades 10-12